java.util.LinkedList源码分析

public class LinkedList<E>

    extends AbstractSequentialList<E>

    implements List<E>, Deque<E>, Cloneable, java.io.Serializable

LinkedList是一个双向链表的实现，允许所有的元素，包括null。

对于index操作，会从链头到链尾地搜索，即使它靠近一个特殊索引位置。

非线程安全的，在多线程环境下，需要外部同步或调用Collections.synchronizedList(new LinkedList(...));获得一个线程安全的链表。

迭代器是快速失败的。

3个实例变量

//链表大小

transient int size = 0;

//链头

transient Node<E> first;

//链尾

transient Node<E> last;

2个构造器

//空链表

public LinkedList() {

}

//根据c创建链表,链表的顺序取决于c的iterator返回元素的顺序

public LinkedList(Collection<? extends E> c) {

    this();

    addAll(c);

}

操作

//返回链表第一个元素

public E getFirst() {

        final Node<E> f = first;

        if (f == null)

            throw new NoSuchElementException();

        return f.item;

}

//返回链表最后一个元素

public E getLast() {

        final Node<E> l = last;

        if (l == null)

            throw new NoSuchElementException();

        return l.item;

}

//删除第一个元素,返回值是第一个元素的值

public E removeFirst() {

        final Node<E> f = first;

        if (f == null)

            throw new NoSuchElementException();

        return unlinkFirst(f);

}

//删除最后一个元素,返回值是最后一个元素

public E removeLast() {

        final Node<E> l = last;

        if (l == null)

            throw new NoSuchElementException();

        return unlinkLast(l);

}

//插入一个元素作为链头

public void addFirst(E e) {

        linkFirst(e);

}

//插入一个元素作为链尾

public void addLast(E e) {

        linkLast(e);

}

//判断链表是否含有o

public boolean contains(Object o) {

        return indexOf(o) != -1;

}

//返回链表大小

public int size() {

        return size;

}

//与addLast的效果一样,在链尾添加一个元素

public boolean add(E e) {

        linkLast(e);

        return true;

}

//删除从链头开始遇到第一个与o等同的元素,如果返回true,表示删除成功

public boolean remove(Object o) {

        if (o == null) {

            for (Node<E> x = first; x != null; x = x.next) {

                if (x.item == null) {

                    unlink(x);

                    return true;

                }

            }

        } else {

            for (Node<E> x = first; x != null; x = x.next) {

                if (o.equals(x.item)) {

                    unlink(x);

                    return true;

                }

            }

        }

        return false;

}

//将c集合的元素添加到链表,插入顺序取决于c的iterator返回的元素顺序

public boolean addAll(Collection<? extends E> c) {

        return addAll(size, c);

}

//在index位置开始将c集合的元素添加到链表,插入顺序取决于c的iterator返回的元素顺序

public boolean addAll(int index, Collection<? extends E> c) {

        checkPositionIndex(index);

        Object[] a = c.toArray();

        int numNew = a.length;

        if (numNew == 0)

            return false;

        Node<E> pred, succ;

        if (index == size) {

            succ = null;

            pred = last;

        } else {

            succ = node(index);

            pred = succ.prev;

        }

        for (Object o : a) {

            @SuppressWarnings("unchecked") E e = (E) o;

            Node<E> newNode = new Node<>(pred, e, null);

            if (pred == null)

                first = newNode;

            else

                pred.next = newNode;

            pred = newNode;

        }

        if (succ == null) {

            last = pred;

        } else {

            pred.next = succ;

            succ.prev = pred;

        }

        size += numNew;

        modCount++;

        return true;

}

//清空链表

public void clear() {

        // Clearing all of the links between nodes is "unnecessary", but:

        // - helps a generational GC if the discarded nodes inhabit

        //   more than one generation

        // - is sure to free memory even if there is a reachable Iterator

        for (Node<E> x = first; x != null; ) {

            Node<E> next = x.next;

            x.item = null;

            x.next = null;

            x.prev = null;

            x = next;

        }

        first = last = null;

        size = 0;

        modCount++;

}

//获取在index位置的元素

public E get(int index) {

        checkElementIndex(index);

        return node(index).item;

}

//将index位置的元素的值修改为element

public E set(int index, E element) {

        checkElementIndex(index);

        Node<E> x = node(index);

        E oldVal = x.item;

        x.item = element;

        return oldVal;

}

//在index位置插入一个element元素

public void add(int index, E element) {

        checkPositionIndex(index);

        if (index == size)

            linkLast(element);

        else

            linkBefore(element, node(index));

}

//删除index位置的元素,返回值是被删除元素的值

public E remove(int index) {

        checkElementIndex(index);

        return unlink(node(index));

}

//返回从链头到链尾第一个遇到与o等同的元素所在的位置,如果不存在返回-1

public int indexOf(Object o) {

        int index = 0;

        if (o == null) {

            for (Node<E> x = first; x != null; x = x.next) {

                if (x.item == null)

                    return index;

                index++;

            }

        } else {

            for (Node<E> x = first; x != null; x = x.next) {

                if (o.equals(x.item))

                    return index;

                index++;

            }

        }

        return -1;

}

//返回从链尾到链头第一个遇到与o等同的元素所在的位置,如果不存在返回-1

public int lastIndexOf(Object o) {

        int index = size;

        if (o == null) {

            for (Node<E> x = last; x != null; x = x.prev) {

                index--;

                if (x.item == null)

                    return index;

            }

        } else {

            for (Node<E> x = last; x != null; x = x.prev) {

                index--;

                if (o.equals(x.item))

                    return index;

            }

        }

        return -1;

}

//返回链头元素值

public E peek() {

        final Node<E> f = first;

        return (f == null) ? null : f.item;

}

//返回链头元素值,如果链表为空,抛出NoSuchElementException

public E element() {

        return getFirst();

}

//返回并删除链头元素值

public E poll() {

        final Node<E> f = first;

        return (f == null) ? null : unlinkFirst(f);

}

//返回并删除链头元素值,如果链表为 空,抛出NoSuchElementException

public E remove() {

        return removeFirst();

}

//在链尾添加元素e

public boolean offer(E e) {

        return add(e);

}

//在链头插入元素e

public boolean offerFirst(E e) {

        addFirst(e);

        return true;

}

//在链尾插入元素e

public boolean offerLast(E e) {

        addLast(e);

        return true;

}

//返回链头元素,如果链表为空,返回null

public E peekFirst() {

        final Node<E> f = first;

        return (f == null) ? null : f.item;

}

//返回链尾元素,如果链表为空,返回null

public E peekLast() {

        final Node<E> l = last;

        return (l == null) ? null : l.item;

}

//返回并删除链头元素

public E pollFirst() {

        final Node<E> f = first;

        return (f == null) ? null : unlinkFirst(f);

}

//返回并删除链尾元素

public E pollLast() {

        final Node<E> l = last;

        return (l == null) ? null : unlinkLast(l);

}

//在链头插入元素e

public void push(E e) {

        addFirst(e);

}

//删除并返回链头元素

public E pop() {

        return removeFirst();

}

//删除从链头到结尾第一个遇到与o等同的元素,如果不存在,什么也不做

public boolean removeFirstOccurrence(Object o) {

        return remove(o);

}

//删除从链尾到链头第一个遇到与o等同的元素,如果不存在,什么也不做

public boolean removeLastOccurrence(Object o) {

        if (o == null) {

            for (Node<E> x = last; x != null; x = x.prev) {

                if (x.item == null) {

                    unlink(x);

                    return true;

                }

            }

        } else {

            for (Node<E> x = last; x != null; x = x.prev) {

                if (o.equals(x.item)) {

                    unlink(x);

                    return true;

                }

            }

        }

        return false;

}

//返回一个列表迭代器,可以向前或向后迭代,index指定起始位置

public ListIterator<E> listIterator(int index) {

        checkPositionIndex(index);

        return new ListItr(index);

}

//返回从链尾开始的迭代器,在ListIterator的基础上实现的

public Iterator<E> descendingIterator() {

        return new DescendingIterator();

}

支持clone

public Object clone() {

        LinkedList<E> clone = superClone();

        // Put clone into "virgin" state

        clone.first = clone.last = null;

        clone.size = 0;

        clone.modCount = 0;

        // Initialize clone with our elements

        for (Node<E> x = first; x != null; x = x.next)

            clone.add(x.item);

        return clone;

}

支持序列化和反序列化

private void writeObject(java.io.ObjectOutputStream s)

        throws java.io.IOException {

        // Write out any hidden serialization magic

        s.defaultWriteObject();

        // Write out size

        s.writeInt(size);

        // Write out all elements in the proper order.

        for (Node<E> x = first; x != null; x = x.next)

            s.writeObject(x.item);

}

private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

        // Read in any hidden serialization magic

        s.defaultReadObject();

        // Read in size

        int size = s.readInt();

        // Read in all elements in the proper order.

        for (int i = 0; i < size; i++)

            linkLast((E)s.readObject());

}

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java.util.LinkedList源码分析

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